1. Field of the Invention
The present invention relates a pressure transducer for sensing a pressure or a differential pressure, and more particularly to a pressure transducer which introduces a pressure in a space for a pressure to be sensed to a pressure transmitting space through a diaphragm and senses the pressure in the space for the pressure to be sensed by a pressure sensitive element disposed in the pressure transmitting space.
2. Description of the Prior Art
The pressure transducer of the type described above transduces the pressure in the pressure transmitting space to a mechanical strain, which is then transduced to an electrical quantity, and it usually uses a vapor deposition type strain gauge or a diffusion type strain gauge. The diffusion type strain gauge is manufactured by diffusing impurity into a silicon base diaphragm, and it is commonly referred to as a semiconductor strain gauge. Since the semiconductor strain gauge has much higher gauge rate than a wire strain gauge, it is widely used in the field of pressure sensing. However, since the semiconductor strain gauge is highly influenced by a temperature, a temperature compensation is needed. For the temperature compensation, it is advisable to arrange a temperature sensitive element such as a thermistor closely to the semiconductor strain gauge. On the other hand, since the pressure transmitting space is filled with liquid such as silicone oil, it is necessary to prevent the change of volume of the liquid by temperature change from affecting to the pressure in the pressure transmitting space. To this end, the volume of the space is designed as small as possible.
The arrangement of electric components such as temperature sensitive element in the pressure transmitting space results in the increase of the volume of the pressure transmitting space because a space for means for holding the electric components is necessary in addition to a space for the electric components. Heretofore, the electric components have been arranged outside the space through a hermetic seal. Since the temperature sensitive element must be located at a position which is subjected to the same temperature as the pressure sensitive element is subjected to, it has been disposed as closely to the pressure sensitive element as possible outside the pressure transmitting space.
Recently, higher presision has been required for the pressure transducer. Where the temperature sensitive element is spaced from the pressure sensitive element by other members like in the prior art transducer, a high precision pressure transducer is not attained because of a temperature difference between both elements due to temperature change in the space for the pressure to be sensed or change of surrounding temperature.